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Characterizing the Ductile-Brittle Transition of Polyamide-11/ Purification and Characterization of Boron Nitride Nanotubes
Kim, William
Kim, William
Abstract
Semi-crystalline polymers undergo a transition from ductile to brittle behavior that has traditionally been characterized by the molecular weight (Mw). However, using Mw as a determinant of the ductile brittle transition has been proven to be imprecise. To better understand the ductile-brittle transition, polyamide-11 (PA-11) was degraded in water and low molecular weight acids: acetic and butanoic. The Mw of PA-11 degraded 4 times faster in acetic and 8 times faster in butanoic acid than when aged in water. This accelerated aging technique separated the role of crystallinity from a changing molecular weight on ductility. This research shows that crystallinity determines the ductile-brittle transition, not the molecular weight. To determine the primary mechanism that causes crystallinity to increase during degradation samples of differing molecular weight were aged in argon. This environment is absent of a degradative species. It tests if polymer chains can rearrange into crystalline regions using only thermal energy, a process called thermal annealing. This research showed that chemicrystallization, not thermal annealing, is the reason for the increase in crystallinity of semi- crystalline polymers. Boron nitride nanotubes (BNNT) have high thermal conductivity as well as the property of being electrically insulating, making them of interest for applications in high power electronics. BNNT contain impurities due to the production process. They must be removed to optimize performance. A procedure of high temperature treatment in a pure oxygen environment was developed and proven to be effective at removing boron impurities from BNNT.
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2018-05-01
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Chemistry